1. Field of the Invention
The present invention relates to a multiple input/output wavelength selective switch device having a plurality of input and output routes provided at an optical node corresponding to a branch point in an optical network in an optical telecommunications field.
2. Discussion of the Related Art
A wavelength division multiplexing optical communication technique is applied to a high-speed and large-capacity optical network that supports today's advanced information-telecommunication society. A ROADM (Reconfigurable Optical Add Drop Multiplexer) device having a reconfigurable add-drop function has been introduced to the optical node corresponding to the branch point in the optical network. To realize the ROADM device, a wavelength selective switch (also referred to as WSS) for switching a desired wavelength to a desired direction has received attention. At present, the wavelength selective switch having the number of input routes N of 1 and the number of output routes M of 2 or more is used. However, to achieve a large-capacity network in future, the node performance is required to improve, and there is a demand for a multiple input/output wavelength selective switch device in which both the number of input routes and the number of output routes are plural.
According to a conventional method, as disclosed in US2008/0138068, it is possible to realize a multiple input/output wavelength selective switch device including N number of 1×M wavelength selective switches connected to input routes and M number of N×1 wavelength selective switches each receiving outputs of the 1×M wavelength selective switches. FIG. 1 is a diagram showing an example of the multiple input/output wavelength selective switch device in which the number of input routes N is four and the number of output routes M is six. In this figure, the multiple input/output wavelength selective switch device has four 1×6 wavelength selective switches (WSS) 110-1 to 110-4 connected to input routes Rin1 to Rin4. Outputs of each of the wavelength selective switches 110-1 to 110-4 are inputted to each of six 4×1 wavelength selective switches 120-1 to 120-6, and selected outputs are outputted from output routes Rout1 to Rout6. Thus, the multiple input/output wavelength selective switch device can be realized.
However, because the wavelength selective switch has a complicated structure, a device area is so large that it cannot be easily mounted on an optical mount board, resulting in an increase in device price. In the configuration shown in this figure, since (N+M) wavelength selective switches are used, disadvantageously, a failure rate is high and transmission reliability is low.
Thus, to realize compact multiple input/output wavelength selective switch with a small number of parts, US2008/0138068 proposes use of a plurality of 2×N wavelength selective switches utilizing inclination of an MEMS (Micro Electric Mechanical System) minute mirror.